1. Field Of The Invention
This invention relates to a method to prevent the growth of algae in swimming pools and spas and to prevent and remove yellow algae stains from surfaces of the pools and spas.
2. Brief Statement Of The Prior Art
Many oxidizing agents have been used with limited success to prevent the growth of algae in swimming pools and spas; and to prevent the formation of yellow algae deposits on the surfaces of the pools and spas.
Examples of agents which have been used are: chlorine, salts and compounds of metals such as silver and copper, quaternary salts, polyquaternary salts, simazines and others. Unfortunately, the microorganisms, after an exposure period of 1 to 3 years, have adapted to these agents, and algae have been reported growing in waters containing 20 ppm chlorine, which is approximately 10 to 15 times the normal dosage level of chlorine in pool and spa waters.
I have discovered that bromine is a very effective algicide in pools and spas. My early work revealed that bromine was effective at dosages as low as 0.1 ppm. I discovered that bromine could be generated in a pool by the addition of a bromide salt, such as sodium bromide, to the pool, provided that the concentration of chlorine or hypochlorite was maintained in the pool during the treatment. In all my early test work, I used a soluble bromide in combination with a polyphosphate as an algicide and have found the combination effective in pools for periods of several years, without any signs that the algae can adapt to the bromine or acquire a tolerance for this agent. My use with the bromide and polyphosphate algicide, however, revealed concentration limits to the polyphosphate coadditive. In my initial work, I used mixtures which contained 25 percent of tetrasodium polyphosphate. This mixture caused clouding of the water when used on a regular maintenance program, in which the composition was added as needed to maintain the bromine content in the effective range. In ny initial work, the composition was also added at a large excess, however, it was found that this caused depletion of chlorine from the pool water, and the present method comprises the frequent addition of limited dosages of the composition to the water.
Bromine has been used as a sanitizer for pools and spas, but not as an algicide. Chloro bromo hydantoin (chloro bromo glycol urea) and a limited amount of a chlorine or hypochlorite releasing agent have been used as a two part additive system, as a sanitizer substitute for chlorine. Also sodium bromide and an oxidant such as oxypersulfate has recently been used as a sanitizer. Elemental bromine has also been used as a sanitizer in combination with a copper sulfate algicide. No mention or claim to the activity of bromine as an algicide has been made by the manufacturers of these products. Indeed, the bromine from these products is not active against algae, as it has not been employed in water which also contains chlorine or hypochlorite.
I have now found that a bromide, added alone to water which contains available chlorine, as chlorine, or as hypochlorite, or other chlorine oxidizers such as trichloro triazine trione, or sodium or potassium dichloro triazine trione, is an effective algicide. I have further found that in some applications, it may not be necessary or even desirable to add a polyphosphate. Accordingly, this invention comprises the use of a bromide salt together with a chlorine-containing oxidizer, as an algicide in a pool or spa, without the concurrent addition of a polyphosphate to the water.